1. Field of the Invention
The present invention relates to semiconductor cleaning and, in particular, to a method and assembly for cleaning and/or removing residues simultaneously from the front side and backside of semiconductor wafers.
2. Description of Related Art
During electronic component fabrication it is common to deposit layers or features of material onto a semiconductor wafer within a semiconductor processing chamber. While most of the chemical by-products and unused reagents are exhausted from the chamber by an exhaust pump, some residue unavoidably deposits on the chamber wall and on other surfaces within the chamber, including both the front side and back side of the processed wafer itself.
Any undesirable residue on the semiconductor process chamber must then be removed to prevent the residue from flaking off and contaminating the electronic device being fabricated. Undesirable residue on the front side and backside of the semiconductor wafer must also be removed to prevent lifting off of such material from the wafer during subsequent semiconductor processing steps, which will ultimately contaminate the semiconductor process chamber and equipment, and in turn, contaminate the wafer.
Semiconductor wafer backside contamination is created during many different semiconductor integrated circuit manufacturing steps such as, for example, coming into contact with the wafer handling/processing equipment. For example, robotic components such as end effectors, wafer chucks and wafer storage devices cause different kinds of particles to be attached to the wafer backside. Also, various chemical processes intended for front side processing of the wafer may affect the backside of the wafer. For example, residues of photo resist polymer may adhere to the wafer backside during lithographic procedures, or even metal contamination of the backside may occur during various types of dry or wet processes. It is essential to remove this wafer backside contamination since it may ultimately reach the wafer's front side, thereby harming sensitive devices, leading to overall yield degradation. Backside contamination can also affect front side planarity causing focus issues and subsequent yield loss in the lithography process.
Proposed schemes for cleaning the wafer backside generally include cleaning or removing residue on the front side of the wafer followed by cleaning of the wafer backside in a separate backside etching or cleaning system. In so doing, once the wafer front side is cleaned, the wafer may be subjected to wafer processing steps prior to cleaning the backside of the wafer. For example, as discussed above, the wafer may undergo wet processing techniques prior to cleaning its backside. In such an event, residue on the wafer backside will lift off during this wet processing causing particles to contaminate the chamber, equipment and wafer front side.
Thus, known techniques of transferring a wafer after the front side is cleaned and/or processed to another processing chamber or system for cleaning the backside of the wafer are undesirable since they are time consuming and require physical contact of the wafer which, again, can lead to front side contamination as well as damaging the wafer itself, leading to still further yield reductions. To date, none of the known wafer cleaning techniques combine the simultaneous cleaning of the wafer front side and backside in a plasma processing chamber so as to eliminate the need for a separate backside etch or strip system, prevent wafer front side contamination, and improve production yields.
Thus, what is needed is a new method and apparatus for wafer backside cleaning.